pkg/libcontainer
Tianon Gravi c54bc4ca04 Remove "root" and "" special cases in libcontainer
These are unnecessary since the user package handles these cases properly already (as evidenced by the LXC backend not having these special cases).

I also updated the errors returned to match the other libcontainer error messages in this same file.

Also, switching from Setresuid to Setuid directly isn't a problem, because the "setuid" system call will automatically do that if our own effective UID is root currently: (from `man 2 setuid`)

    setuid() sets the effective user ID of the calling process.  If the
    effective UID of the caller is root, the real UID and saved set-user-
    ID are also set.

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
2014-04-28 16:46:03 -06:00
..
console Move rest of console functions to pkg 2014-04-24 10:35:20 -07:00
mount Move mounts into types.go 2014-04-24 10:35:20 -07:00
network Fix libcontainer network support on rhel6 2014-04-09 15:44:18 +02:00
nsinit Remove "root" and "" special cases in libcontainer 2014-04-28 16:46:03 -06:00
security Ignore isnot exists errors for proc paths 2014-04-24 10:35:20 -07:00
utils Refactor and improve libcontainer and driver 2014-02-24 21:11:52 -08:00
container.go Move mounts into types.go 2014-04-24 10:35:20 -07:00
container.json Update container.json and readme 2014-04-24 10:35:20 -07:00
MAINTAINERS Update email + add self to pkg/signal 2014-03-10 20:26:45 -07:00
README.md Update container.json and readme 2014-04-24 10:35:20 -07:00
TODO.md Update libcontainer readme and todo list 2014-03-13 15:18:08 -07:00
types.go Move mounts into types.go 2014-04-24 10:35:20 -07:00
types_linux.go Dont use custom marshaling for caps and namespaces 2014-03-20 23:09:01 +00:00
types_test.go Avoid "invalid memory address or nil pointer dereference" panic 2014-04-10 22:07:29 +09:00

libcontainer - reference implementation for containers

background

libcontainer specifies configuration options for what a container is. It provides a native Go implementation for using Linux namespaces with no external dependencies. libcontainer provides many convenience functions for working with namespaces, networking, and management.

container

A container is a self contained directory that is able to run one or more processes without affecting the host system. The directory is usually a full system tree. Inside the directory a container.json file is placed with the runtime configuration for how the processes should be contained and ran. Environment, networking, and different capabilities for the process are specified in this file. The configuration is used for each process executed inside the container.

Sample container.json file:

{
   "mounts" : [
      {
         "type" : "devtmpfs"
      }
   ],
   "tty" : true,
   "environment" : [
      "HOME=/",
      "PATH=PATH=$PATH:/bin:/usr/bin:/sbin:/usr/sbin",
      "container=docker",
      "TERM=xterm-256color"
   ],
   "hostname" : "koye",
   "cgroups" : {
      "parent" : "docker",
      "name" : "docker-koye"
   },
   "capabilities_mask" : [
      {
         "value" : 8,
         "key" : "SETPCAP",
         "enabled" : false
      },
      {
         "enabled" : false,
         "value" : 16,
         "key" : "SYS_MODULE"
      },
      {
         "value" : 17,
         "key" : "SYS_RAWIO",
         "enabled" : false
      },
      {
         "key" : "SYS_PACCT",
         "value" : 20,
         "enabled" : false
      },
      {
         "value" : 21,
         "key" : "SYS_ADMIN",
         "enabled" : false
      },
      {
         "value" : 23,
         "key" : "SYS_NICE",
         "enabled" : false
      },
      {
         "value" : 24,
         "key" : "SYS_RESOURCE",
         "enabled" : false
      },
      {
         "key" : "SYS_TIME",
         "value" : 25,
         "enabled" : false
      },
      {
         "enabled" : false,
         "value" : 26,
         "key" : "SYS_TTY_CONFIG"
      },
      {
         "key" : "AUDIT_WRITE",
         "value" : 29,
         "enabled" : false
      },
      {
         "value" : 30,
         "key" : "AUDIT_CONTROL",
         "enabled" : false
      },
      {
         "enabled" : false,
         "key" : "MAC_OVERRIDE",
         "value" : 32
      },
      {
         "enabled" : false,
         "key" : "MAC_ADMIN",
         "value" : 33
      },
      {
         "key" : "NET_ADMIN",
         "value" : 12,
         "enabled" : false
      },
      {
         "value" : 27,
         "key" : "MKNOD",
         "enabled" : true
      }
   ],
   "networks" : [
      {
         "mtu" : 1500,
         "address" : "127.0.0.1/0",
         "type" : "loopback",
         "gateway" : "localhost"
      },
      {
         "mtu" : 1500,
         "address" : "172.17.42.2/16",
         "type" : "veth",
         "context" : {
            "bridge" : "docker0",
            "prefix" : "veth"
         },
         "gateway" : "172.17.42.1"
      }
   ],
   "namespaces" : [
      {
         "key" : "NEWNS",
         "value" : 131072,
         "enabled" : true,
         "file" : "mnt"
      },
      {
         "key" : "NEWUTS",
         "value" : 67108864,
         "enabled" : true,
         "file" : "uts"
      },
      {
         "enabled" : true,
         "file" : "ipc",
         "key" : "NEWIPC",
         "value" : 134217728
      },
      {
         "file" : "pid",
         "enabled" : true,
         "value" : 536870912,
         "key" : "NEWPID"
      },
      {
         "enabled" : true,
         "file" : "net",
         "key" : "NEWNET",
         "value" : 1073741824
      }
   ]
}

Using this configuration and the current directory holding the rootfs for a process, one can use libcontainer to exec the container. Running the life of the namespace, a pid file is written to the current directory with the pid of the namespaced process to the external world. A client can use this pid to wait, kill, or perform other operation with the container. If a user tries to run a new process inside an existing container with a live namespace, the namespace will be joined by the new process.

You may also specify an alternate root place where the container.json file is read and where the pid file will be saved.

nsinit

nsinit is a cli application used as the reference implementation of libcontainer. It is able to spawn or join new containers giving the current directory. To use nsinit cd into a Linux rootfs and copy a container.json file into the directory with your specified configuration.

To execute /bin/bash in the current directory as a container just run:

nsinit exec /bin/bash

If you wish to spawn another process inside the container while your current bash session is running just run the exact same command again to get another bash shell or change the command. If the original process dies, PID 1, all other processes spawned inside the container will also be killed and the namespace will be removed.

You can identify if a process is running in a container by looking to see if pid is in the root of the directory.